Your probation will be revoked and your original sentence will be reinstated or imposed – in addition to your new charges!

Other Answer(2) :

You will go to jail for probation violation.

Depending on the judge, but basically by failing the original deal is OVER: it can mean jail (on a jail for minors), no license, more fines or a MUCH longer probation.

Most of the time when a charge is lowered toa lesser offence is based on the assumption that you wont fail your probation; once you fail your probation they can in theory up your chages to DUI again and cange your original punishment.